Selecting a WAN Technology

The CCDA objectives covered in this section are the following:

18 Recognize scalability constraints and issues for standard WAN

technologies.

20 Recommend Cisco products and WAN technologies that will meet the customer's requirements for performance, capacity, and scalability in an enterprise network.

To simplify the process for choosing the right WAN technology, Table 5-1 summarizes important aspects of common WAN technologies into a reference chart. Table 5-1 contains information on which technology is the most appropriate for certain situations, as well as important features and specifications.

Table 5-1 Identifying the Appropriate WAN Technology WAN Technology Applications

Analog modem Used by telecommuters and dial-up mobile users.

Average usage is less than 2 hours per day.

Line speeds of 56 Kbps or less.

Used for backup for another type of link.

Can be attached to network devices such as a router for remote access and configuration.

Customer is charged for usage of line.

DSL Uses existing copper telephone lines to usually provide up to 1.544-Mbps speeds to the home or remote office.

xDSL refers to the family of DSL technologies.

An excellent reference on how DSL works can be found at http:// www.netspeed.com/overview.html.

Cable modem These are data connections through the same line as cable TV. Possible bandwidth for Internet access can be up to 27 Mbps; however, actual bandwidth would depend on how populated the cable line is.

An excellent reference on cable modems can be found at http:// www.cable-modems.org/tutorial/.

Table 5-1 Identifying the Appropriate WAN Technology (Continued) WAN Technology Applications

Leased line Used in point-to-point networks and hub-and-spoke topologies.

Common leased lines are fractional T1 (less than 1.544 Mbps), T1 (1.544 Mbps), and T3 (44.736 Mbps).

Used as backup for other high-speed links.

T1s are commonly used for corporate Internet connections.

Customer pays for dedicated line.

ISDN Basic Rate Interface (BRI) is composed of two 64-Kbps B (bearer)

channels and one 16-Kbps D (delta) channel

Cost-effective remote access for corporate or telecommuters.

Supports voice and video.

Used as backup for leased line and Frame Relay links.

Customer is charged for usage of line.

Frame Relay Cost-effective, high-speed, low-latency mesh or hub-and-spoke topology between remote sites.

Used for remote offices and LANs.

Common line speeds are fractional T1 to T1.

Both private and carrier-provided networks.

Customer is charged for usage of line.

X.25 WAN circuit or backbone with Layer 3 reliability features.

Support for legacy applications.

ATM Support for accelerating bandwidth requirements.

Support for multiple quality of service classes for differing application requirements for delay and loss.

Supports voice, video, and data.

Used on top of T3, SONET, and other high-speed lines.

Customer pays for the dedicated line.

A key design consideration for WAN implementations is cost. The costs associated with WAN connections can vary depending on the implementation. The cost associated with establishing a WAN connection can have multiple variables. For example, in the chart above, Frame Relay is described as a technology where the customer pays for the access on a usage basis. The cost of usage is charged in addition to the cost for access to the Frame Relay network. An example of this type of charge is a monthly phone bill. Every month you pay a flat access fee for having the phone service, and in addition, you are charged for certain specific phone calls. These factors contribute to the high cost of WAN access.

There are four basic methods to manage costs for WAN connections. The first is negotiating with carriers to find inexpensive and competitive pricing for bandwidth. The increase in competition within the carrier market has made shopping for inexpensive bandwidth even easier. The second method to manage costs is optimizing WAN lines by controlling traffic and by optimizing the WAN design to best use the bandwidth. The third method to manage costs is the integration of multiple services across the same bandwidth, such as voice, data, and video. The final method incorporates quality of service issues.

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